In recent years, the usage of LED illumination instead of other kinds of illumination (such as the fluorescent illumination, incandescent bulb illumination, and the like), has significantly increased due to the increasing luminosity of LED devices and due to their continuously decreasing costs. Although most people around the world still use fluorescent and incandescent bulb lighting, development of low-cost and efficient LED illuminating devices has recently accelerated rapidly.
Nowadays, various lighting devices include light dimmers, which enable adjusting the power delivered to the light sources, and thereby enable the control of the amount of light generated by these light sources. For this, the user interface of dimmers is usually equipped with an appropriate light adjustment mechanism (e.g., a slider). During such an adjustment, the light outputted from the light sources (e.g., LEDs) is gradually varied, enabling the user to adjust the desired level of illumination, which is the most appropriate for his needs, and to switch said light sources ON and OFF.
According to the prior art, conventional lighting devices are usually powered by an AC source (line voltage power, such as 120V RMS (Root Mean Square) at 60 Hz (Hertz) and 220V at 50 Hz); therefore, AC dimmers usually receive the AC line voltage at their input, and then output corresponding AC signals, having one or more variable parameters used to adjust an average voltage of these AC signals in response to a user's operation of the dimmer. Conventional AC dimmers are configured to control the power delivered to light sources in several different ways, such as increasing/decreasing voltage amplitude of the AC output signal and adjusting the duty cycle of the AC output signal (for example, by chopping-out portions of the AC voltage cycle). This technique is sometimes called phase/angle modulation, since it is based on the adjustable phase angle of the AC output signal. Usually, dimmers that implement such angle modulation use a TRIAC component/unit that is selectively operated to adjust the duty cycle of the AC signal outputted from the dimmer, and thereby to modulate the phase angle. Such dimmers are therefore called “TRIAC dimmers”.
Also, according to the prior art, the early technology in the field of LED illumination was based on providing a DC (Direct Current) power supply and then using a microprocessor to operate a PWM (Pulse Width Modulation) switch to control the brightness of the perceived light. On the other hand, in the fields of fluorescent and incandescent bulb lighting, the control of light has long been available by using phase control dimmers, such as the TRIAC dimmers. However, the use of TRIAC dimmers for other than incandescent lighting requires the overcoming of several problems, such as TRIAC instability.
The problems related to providing LED illumination have been recognized in the Prior Art, and various systems and methods have been developed to provide a solution.
U.S. Pat. No. 6,586,890 discloses a driver circuit that provides power to LEDs by using pulse width modulation (PWM). The driver circuit uses current feedback to adjust power to LED arrays and provides a full light and a dim mode.
U.S. Pat. No. 5,783,909 describes a method of controlling the light output from a LED by using PWM control of the LED current in response to signals provided from a light sensor, in order that the generated light will remain constant.
U.S. Pat. No. 6,788,011 presents systems and methods related to LED systems capable of generating light, such as for illumination or display purposes. The light-emitting LEDs may be controlled by a processor to alter the brightness and/or color of the generated light, e.g., by using pulse-width modulated signals. Thus, according to U.S. Pat. No. 6,788,011, the resulting illumination may be controlled by a computer program to provide complex, pre-designed patterns of light.
U.S. Pat. No. 7,038,399 relates to methods and apparatus for providing power to devices via an AC (Alternating Current) power source, and for facilitating the use of LED-based light sources on AC power circuits that provide signals other than standard line voltages. In one example, LED-based light sources may be coupled to AC power circuits that are controlled by conventional dimmers.
U.S. Pat. No. 6,744,223 discloses a multicolor lamp system that includes a dimming circuit and an illumination module electrically connected to the dimming circuit. The illumination module has a detection circuit for detecting the output of the dimming circuit. The detection circuit generates a detection signal corresponding to the output of the dimming circuit. A microcontroller is programmed to receive the detection signal and to supply a corresponding electrical signal to a plurality of LEDs.
U.S. Pat. No. 5,604,411 presents a dimming ballast for use with a phase control dimmer, including an EMI filter to avoid excessive voltage and peak currents in the filter due to resonance with the phase controlled AC waveform at low conduction angles, when the load presented by the lamp is low. The ballast includes circuitry to sense the rectified DC voltage and to discharge the filter capacitor when the rectified voltage is at or near zero, to thereby keep the EMI filter loaded and prevent misfiring of the phase control dimmer.
There is a continuous need in the art to enable the high quality dimming of light (e.g., generated by a LED load) by using a TRIAC dimmer that includes a TRIAC component/unit, substantially overcoming TRIAC component instability issues. Also, there is a need in the art to provide a phase controlled dimming LED driver, which eliminates the need to use a processing unit (e.g., a microprocessor, a microcontroller), and which pulse width modulates the output current provided to the LED load at a frequency unrelated to the power line frequency. In addition, there is a need to achieve “deep” dimming by using a TRIAC dimmer (e.g., dimming down to 0.1% of the full light brightness) and enabling keeping the TRIAC component of the TRIAC dimmer operating in a substantially stable manner. Further, there is a need to enable assembling LED drivers for color mixing, in which two or more separate LED drivers can be independently controlled by phase control dimmers (e.g., by TRIAC dimmers), so that any desired color light can be generated.